1. Field of the Invention
The present invention relates to a backlight unit as surface light source function and particularly improvement of support structure for light guide plate, and further the present invention relates to a crystal display device having the same.
2. Description of the Prior Art
In recent years, as the display devices of such information machines as laptop personal computers and word processors and the display devices of such image machines as portable television sets, video movies, and car navigation systems, the liquid crystal display (LCD) devices have come to be used in more cases than not with a view to utilizing such features as lightness, thinness, and low power consumption. For the most part, these liquid crystal display devices having a backlight unit such as a lighting unit throw a light on a liquid crystal display panel from behind.
Lighting method of backlight unit is classified an edge light method and a direct under light method. An edge light method which comprises placing a light guide plate behind a display element, and output a point light using as a LED (light-emitting diode) or a linear light using as a fluorescent discharge tube, for example. A direct under light method which comprises placing a light diffuser plate behind a display element, and output plural linear light using as plural fluorescent discharge tubes, for example. Generally, an edge light method is better than a direct under light method, concerning thin thickness body. Thus, an edge light method is suitable for personal digital assistance (PDA), and laptop personal computer.
A backlight unit used an edge light method that needs holding a light guide plate and a light part by a frame belongs to the backlight unit. For example, a light guide plate sandwiched between the frame and a back cover belongs to the backlight unit is proposed. For example, a light guide plate fixed to the frame by double-sided adhesive tape is proposed. The light guide plate sandwiched structure is preferable, because it doesn't use additional double-sided adhesive tape and easy to assemble.
As above structure that needs setting the light guide plate near the light part. The light guide plate approximate to the light part, it can be inducing a light of the light part to the light guide plate high efficiency, and prevent to uneven luminance occurs.
Therefore, prior art proposed that the frame having a press-supporting part (See JP2003-215546A). Prior art JP2003-215546A is disclosed a LCD device having a plastic frame which enclosed a light guide plate and a LED; wherein the plastic frame comprises a elastic press-supporting part such as a plastic spring; wherein the press-supporting part is formed on a edge of the frame and the edge is opposite to the LED, and the press-supporting part press the light guide plate to the LED.
However, in the above method by using the prior art JP2003-215546A, it is easy to occur pressing defective at the press-supporting part under wide temperature range of external environment. The plastic frame comprises the plastic spring part is sensitive temperature changes. The plastic frame is easy to stretch and deform by temperature changes. Function of the press-supporting part is damaged by the plastic frame stretched or the plastic frame deformed. That is, the light guide plate is pressed by the press-supporting part under the room temperature, but the press-supporting part is deformed by temperature raised and the press-supporting part couldn't press to the light guide plate, then the light guide plate is easy to move inside of the plastic frame. Backlash of the light guide plate is significantly impairing the commercial value and image disqualify such as uneven luminance occurs. For example, the LCD device having the prior art structure and installed a car navigation system, backlash of the light guide plate occurs and image disqualify such as uneven luminance occurs. Because, the room temperature of the car sometimes rising high temperature.
As structure of prior art JP2003-215546A which comprises a frame having a press-supporting part such as a plastic spring and press and support to the light guide plate. It is necessary to set the plastic springs on each side of the plastic frame for pressing as horizontally and vertically if keep stable supporting condition. But, it is difficult to assemble the light guide plate into the plastic frame when the plastic springs are set on each side of the plastic frame. In case of the plastic springs are set on horizontally sides or the plastic springs are set on vertically sides, the position of the light guide plate is unsettled. Therefore, the LCD device having the prior art structure occurs image disqualify.
The present invention has been proposed in view of the conventional actual situation, and the object thereof is to provide a backlight unit which structure is certain pressing the light guide plate to the light part such as LED without being influenced by external environment, and prevent to occurs image disqualify such as uneven luminance and easy to assemble the light guide plate. In addition, the object thereof is to provide a liquid crystal display (LCD) device having the backlight unit.